A turbo-prop can be equipped with a pitch controlling system associated with each of the blades of its propeller, so as to adapt the orientation of the blades to the speed of the aircraft.
Such a system is designed such that the incidence of the blade remains fixed when the control system is not actuated, and must therefore make it possible to resist the action of the torque generated by the aerodynamic and centrifugal forces exerted on said blade during rotation of the propeller. More generally, to keep its pitch, it is considered that the blade must be locked in both directions of rotation along its own axis. To do this, the system is generally equipped with a locking mechanism, usually of the type ensuring contact/friction between two parts, such as a disc brake. To control the incidence of the blade, it is therefore necessary to perform a preliminary step for unblocking the incidence of the blade, by breaking the contact between the two parts of the locking mechanism.
Of course, the presence of the locking mechanism greatly complexifies the design of the control system, which creates drawbacks in terms of mass, reliability and bulk.